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| author | Uros Bizjak <ubizjak@gmail.com> | 2022-06-24 16:14:12 +0200 |
|---|---|---|
| committer | akpm <akpm@linux-foundation.org> | 2022-07-17 17:31:38 -0700 |
| commit | 43c249ea0b1e10baac4a1264a25d69723ce5d2c2 (patch) | |
| tree | 338054a85d0960a804cef2785306515411dab120 /include/linux/compiler-gcc.h | |
| parent | 86e5908ec293bf6505a59d02542da006226bcaa7 (diff) | |
| download | linux-43c249ea0b1e10baac4a1264a25d69723ce5d2c2.tar.gz linux-43c249ea0b1e10baac4a1264a25d69723ce5d2c2.tar.bz2 linux-43c249ea0b1e10baac4a1264a25d69723ce5d2c2.zip | |
compiler-gcc.h: remove ancient workaround for gcc PR 58670
The workaround for 'asm goto' miscompilation introduces a compiler barrier
quirk that inhibits many useful compiler optimizations. For example,
__try_cmpxchg_user compiles to:
11375: 41 8b 4d 00 mov 0x0(%r13),%ecx
11379: 41 8b 02 mov (%r10),%eax
1137c: f0 0f b1 0a lock cmpxchg %ecx,(%rdx)
11380: 0f 94 c2 sete %dl
11383: 84 d2 test %dl,%dl
11385: 75 c4 jne 1134b <...>
11387: 41 89 02 mov %eax,(%r10)
where the barrier inhibits flags propagation from asm when compiled with
gcc-12.
When the mentioned quirk is removed, the following code is generated:
11553: 41 8b 4d 00 mov 0x0(%r13),%ecx
11557: 41 8b 02 mov (%r10),%eax
1155a: f0 0f b1 0a lock cmpxchg %ecx,(%rdx)
1155e: 74 c9 je 11529 <...>
11560: 41 89 02 mov %eax,(%r10)
The refered compiler bug:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
was fixed for gcc-4.8.2.
Current minimum required version of GCC is version 5.1 which has the above
'asm goto' miscompilation fixed, so remove the workaround.
Link: https://lkml.kernel.org/r/20220624141412.72274-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'include/linux/compiler-gcc.h')
| -rw-r--r-- | include/linux/compiler-gcc.h | 11 |
1 files changed, 0 insertions, 11 deletions
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index a0c55eeaeaf1..9b157b71036f 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -66,17 +66,6 @@ __builtin_unreachable(); \ } while (0) -/* - * GCC 'asm goto' miscompiles certain code sequences: - * - * http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670 - * - * Work it around via a compiler barrier quirk suggested by Jakub Jelinek. - * - * (asm goto is automatically volatile - the naming reflects this.) - */ -#define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0) - #if defined(CONFIG_ARCH_USE_BUILTIN_BSWAP) #define __HAVE_BUILTIN_BSWAP32__ #define __HAVE_BUILTIN_BSWAP64__ |